1. Field of the Invention
The present invention relates to hinge devices to be used for a foldable apparatus comprising a first body and a second body, and particularly to a hinge device which holds the first body to any intermediary angular position relative to the second body between a fully closed position and the fully opened position, and stays the first body at a certain intermediary angular position.
2. Description of the Related Art
A conventional hinge device is disclosed in Japanese Patent Publication No. 1-212052, which is used for a portable telephone. The hinge device comprises a lot of discrete elements which need to be assembled to the portable telephone one by one. It makes the assembling process unduly cumbersome.
Another conventional hinge device is disclosed in U.S. Pat. No. 6,305,050, which is used for a portable telephone comprising a fixed disk of a main body and a movable disk of a cover. The movable disk resiliently abuts the fixed disk under an effect of a coil spring. The fixed disk defines a plurality of recesses in an abutment facet of the movable disk. The movable disk forms a plurality of engaging projections for engaging in the recesses of the fixed disk. The process of assembling the hinge device to the portable telephone is simplified, because the hinge device is assembled before being attached to the portable telephone. However, it suffers from sliding friction when the projections climb up the recesses. The abutment facet is prone to be worn because of the sliding friction. After many-times opening and closing operations, the projections and the recesses will get abrasion, which causes worse effect of holding and staying of the cover. In particularly, the friction areas are fixed in this hinge device, so the hinge device at these areas is easier to be abraded, therefore shortening the life span of the hinge device.
Thus, a hinge device for a foldable apparatus which solves the above-mentioned problems is strongly desired.